Display screen or portion thereof with transitional graphical user interface



FIG. 1 is a front view of a display screen or portion thereof with transitional graphical user interface showing the new design; and,

FIG. 2 is a front view of a second image thereof.

The appearance of the transitional image sequentially transitions between the images shown in FIGS. 1 and 2. No ornamental aspects are associated with the process or period in which one image transitions to another image.

The broken lines showing the display screen or portion thereof and all text and icons of the graphical user interface form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with transitional graphical user interface, as shown and described. 